I realise a lot of these changes could never happen in Core, given that 'what's written in the manual can't be changed', but my thoughts on the railgun is that it's the wrong ability. Thematically, I would actually fiddle the Marza and the Kol's abilities together.
- The Marza loses Radiation Bomb, gains a modified Railgun ability. Why? Because it's got a sodding great spinal mounted mass driver - it's used for Raze Planet, why not let it do something similar to ships?
- The Kol loses the Railgun, gains an AOE weapon - something like Radiation Bomb, although given it's straight-up-no-surprises, toe-to-toe combatant style, probably a flat AOE explosion rather than a DoT ability - thematically, it makes as much sense as a Railgun for the Kol to be the TEC warship that carries high velocity nuclear warheads...
I'd also up the laser damage. Whether that's the totally-awesome-visuals laser beams, or the laser cannon (Which really does look like a waste of space half the time - both visually and DPS) is debatable, but a moderate boost to one or the other would help bring it up to Marza levels of threat, at least tactically if not strategically - as it is, other than Flak Burst, why target it first? You've got a tough brick that can't actually attract hostile fire. Might wanna look into that. 
A minor idea that amuses me, though I doubt it'd come about, could be swapping its laser cannons for an actual railgun - you know, like the Guass Turrets. While this would do slightly unusual things to its buff potential (+15% rate of fire and +12% range being the two buffs it'd get), this could nonetheless give it a little quirk of being 'different' (and justify the size of the turret it fires from). And who knows? A +12% range might let it get off 'parting shots' on fleeing opponents. *shrug* The thought amuses, but is far from essential. 